I have an ST30 and I have never experiences any IR. No IR at any time of using my plasma. I would say I have about close to 600 or more hours on it. Now of course, I have seen remnants of some opaque logos or still graphics that I recently watched on a blank no input channel, but that is not IR and can never be seen watching normal content.
Many people here are paranoid about burn in—I am not directing this at you by the way— but if you simply see to balancing your content then all should be fine. Everyone here can argue all day about proper break-in techniques do's and don'ts, but at the end of the day it's about a reasonable amount of balance. Just the other day, I watched the History Channel for about 6 hours straight. The next day just to keep on top of the balance, I put my ST30 on HBO, put it in zoom mode and let it go for a 3 hours until automatic shut off kicked in.